A transmission method for transmitting digital signals includes a single end signal transmission and a differential signal transmission. In the differential signal transmission, noises applied in common to two lines offset each other. Therefore, a noise immunity is high. Therefore, a signal amplitude is made small to enable a high speed signal transmission. However, the amount of a signal line for the differential signal transmission is required to be two times the amount of a signal line for the single end signal transmission. Therefore, in a case where lines are disposed for many signals (in a case where a restriction of a cost, a volume, or a weight is strong) the single end signal transmission is frequently used.
On the other hand, a connector is used to electrically connect multiple modules, for example. Because a conventional connector has a structure of causing electrodes to be mutually attached by pressure, a problem of reliability or the like may occur.
As a means for solving this problem, a noncontact connector (an EM connector) including a directional coupler for transmitting a signal by an electromagnetic coupling is known. Because the directional coupler may cause only a high frequency signal component to pass, a pulse signal having a small amplitude is output when a digital signal is input. From the pulse signal, the original digital signal is recovered using a reception circuit including a comparison circuit and a signal hold circuit.